Fine grained permissions

Before Trac 0.11, it was only possible to define fine-grained permissions checks on the repository browser sub-system.

Since 0.11, there's a general mechanism in place that allows custom permission policy plugins to grant or deny any action on any kind of Trac resources, even at the level of specific versions of such resources.

Note that for Trac 0.12, authz_policy has been integrated as an optional module (in tracopt.perm.authz_policy.*), so it's installed by default and can simply be activated via the Plugins panel in the Trac administration module.

Permission Policies

A great diversity of permission policies can be implemented, and Trac comes with a few examples.

Which policies are currently active is determined by a configuration setting in TracIni:
e.g.

This lists the #ReadonlyWikiPolicy which controls readonly access to wiki pages, followed by the DefaultPermissionPolicy which checks for the traditional coarse grained style permissions described in TracPermissions, and the LegacyAttachmentPolicy which knows how to use the coarse grained permissions for checking the permissions available on attachments.

Among the possible optional choices, there is #AuthzPolicy, a very generic permission policy, based on an Authz-style system. See
​authz_policy.py for details.

Another popular permission policy #AuthzSourcePolicy, re-implements the pre-0.12 support for checking fine-grained permissions limited to Subversion repositories in terms of the new system.

AuthzPolicy

Configuration

Put a ​authzpolicy.conf file somewhere, preferably on a secured location on the server, not readable for others than the webuser. If the file contains non-ASCII characters, the UTF-8 encoding should be used.

Usage Notes

Note that the order in which permission policies are specified is quite critical,
as policies will be examined in the sequence provided.

A policy will return either True, False or None for a given permission check. True is returned if the policy explicitly grants the permission. False is returned if the policy explicitly denies the permission. None is returned if the policy is unable to either grant or deny the permission.

NOTE: Only if the return value is None will the next permission policy be consulted.
If none of the policies explicitly grants the permission, the final result will be False
(i.e. permission denied).

Each section of the config is a glob pattern used to match against a Trac resource
descriptor. These descriptors are in the form:

<realm>:<id>@<version>[/<realm>:<id>@<version> ...]

Resources are ordered left to right, from parent to child. If any
component is inapplicable, * is substituted. If the version pattern is
not specified explicitely, all versions (@*) is added implicitly

# A single repository:
[repository:test_repo@*]
john = BROWSER_VIEW, FILE_VIEW
# John has BROWSER_VIEW and FILE_VIEW for the entire test_repo
# The default repository (requires Trac 1.0.2 or later):
[repository:@*]
john = BROWSER_VIEW, FILE_VIEW
# John has BROWSER_VIEW and FILE_VIEW for the entire default repository
# All repositories:
[repository:*@*]
jack = BROWSER_VIEW, FILE_VIEW
# Jack has BROWSER_VIEW and FILE_VIEW for all repositories

Very fine grain repository access:

# John has BROWSER_VIEW and FILE_VIEW access to trunk/src/some/location/ only
[repository:test_repo@*/source:trunk/src/some/location/*@*]
john = BROWSER_VIEW, FILE_VIEW
# John has BROWSER_VIEW and FILE_VIEW access to only revision 1 of all files at trunk/src/some/location only
[repository:test_repo@*/source:trunk/src/some/location/*@1]
john = BROWSER_VIEW, FILE_VIEW
# John has BROWSER_VIEW and FILE_VIEW access to all revisions of 'somefile' at trunk/src/some/location only
[repository:test_repo@*/source:trunk/src/some/location/somefile@*]
john = BROWSER_VIEW, FILE_VIEW
# John has BROWSER_VIEW and FILE_VIEW access to only revision 1 of 'somefile' at trunk/src/some/location only
[repository:test_repo@*/source:trunk/src/some/location/somefile@1]
john = BROWSER_VIEW, FILE_VIEW

Note: In order for Timeline to work/visible for John, we must add CHANGESET_VIEW to the above permission list.

Missing Features

Although possible with the DefaultPermissionPolicy handling (see Admin panel), fine-grained permissions still miss those grouping features (see ​#9573, ​#5648). Patches are partially available, see forgotten authz_policy.2.patch part of ​#6680).

AuthzSourcePolicy (mod_authz_svn-like permission policy)

At the time of this writing, the old fine grained permissions system from Trac 0.11 and before used for restricting access to the repository has been converted to a permission policy component, but from the user point of view, this makes little if no difference.

That kind of fine-grained permission control needs a definition file, which is the one used by Subversion's mod_authz_svn.
More information about this file format and about its usage in Subversion is available in the ​Path-Based Authorization section in the Server Configuration chapter of the svn book.

/branches/calc/bug-142/secret = harry has no access, sally has read access (inherited as a sub folder permission)

Trac Configuration

To activate fine grained permissions you must specify the authz_file option in the [trac] section of trac.ini. If this option is set to null or not specified the permissions will not be used.

[trac]
authz_file = /path/to/svnaccessfile

If you want to support the use of the [modulename:/some/path] syntax within the authz_file, add

authz_module_name = modulename

where modulename refers to the same repository indicated by the repository_dir entry in the [trac] section. As an example, if the repository_dir entry in the [trac] section is /srv/active/svn/blahblah, that would yield the following:

Since 1.1.2, the read-only attribute of wiki pages is enabled and enforced when ReadonlyWikiPolicy is in the list of active permission policies. The default for new Trac installations in 1.1.2 and later is:

When upgrading from earlier versions of Trac, ReadonlyWikiPolicy will be appended to the list of permission_policies when upgrading the environment, provided that permission_policies has the default value. If any non-default permission_polices are active, ReadonlyWikiPolicywill need to be manually added to the list. A message will be echoed to the console when upgrading the environment, indicating if any action needs to be taken.

ReadonlyWikiPolicy must be listed before DefaultPermissionPolicy. The latter returns True to allow modify, delete or rename actions when the user has the respective WIKI_* permission, without consideration for the read-only attribute.

The ReadonlyWikiPolicy returns False to deny modify, delete and rename actions on wiki pages when the page has the read-only attribute set and the user does not have WIKI_ADMIN, regardless of WIKI_MODIFY, WIKI_DELETE and WIKI_RENAME permissions. It returns None for all other cases.

When active, the #AuthzPolicy should therefore come before ReadonlyWikiPolicy, allowing it to grant or deny the actions on individual resources, which is the usual ordering for AuthzPolicy in the permission_policies list.

The placement of #AuthzSourcePolicy relative to ReadonlyWikiPolicy does not matter since they don't perform checks on the same realms.

For all other permission policies, the user will need to decide the proper ordering. Generally, if the permission policy should be capable of overriding the check performed by ReadonlyWikiPolicy, it should come before ReadonlyWikiPolicy in the list. If the ReadonlyWikiPolicy should override the check performed by another permission policy, as is the case for DefaultPermissionPolicy, then ReadonlyWikiPolicy should come first.

Debugging permissions

In trac.ini set:

[logging]
log_file = trac.log
log_level = DEBUG
log_type = file

And watch:

tail -n 0 -f log/trac.log | egrep '\[perm\]|\[authz_policy\]'

to understand what checks are being performed. See the sourced documentation of the plugin for more info.